全文获取类型
收费全文 | 12222篇 |
免费 | 1033篇 |
国内免费 | 1205篇 |
专业分类
化学 | 8459篇 |
晶体学 | 250篇 |
力学 | 524篇 |
综合类 | 101篇 |
数学 | 1346篇 |
物理学 | 3780篇 |
出版年
2023年 | 74篇 |
2022年 | 173篇 |
2021年 | 345篇 |
2020年 | 299篇 |
2019年 | 280篇 |
2018年 | 296篇 |
2017年 | 296篇 |
2016年 | 378篇 |
2015年 | 428篇 |
2014年 | 517篇 |
2013年 | 853篇 |
2012年 | 983篇 |
2011年 | 1094篇 |
2010年 | 760篇 |
2009年 | 668篇 |
2008年 | 929篇 |
2007年 | 847篇 |
2006年 | 761篇 |
2005年 | 722篇 |
2004年 | 595篇 |
2003年 | 444篇 |
2002年 | 463篇 |
2001年 | 379篇 |
2000年 | 358篇 |
1999年 | 221篇 |
1998年 | 104篇 |
1997年 | 115篇 |
1996年 | 134篇 |
1995年 | 118篇 |
1994年 | 119篇 |
1993年 | 82篇 |
1992年 | 76篇 |
1991年 | 60篇 |
1990年 | 62篇 |
1989年 | 57篇 |
1988年 | 35篇 |
1987年 | 21篇 |
1986年 | 17篇 |
1985年 | 33篇 |
1984年 | 27篇 |
1983年 | 25篇 |
1982年 | 28篇 |
1981年 | 21篇 |
1980年 | 18篇 |
1979年 | 19篇 |
1978年 | 20篇 |
1977年 | 10篇 |
1976年 | 13篇 |
1975年 | 10篇 |
1972年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Laser welding is one of the most precise welding processes in joining sheet metals. In laser welding, performing real time evaluation of the welding quality is very important to enhance the efficiency of the welding process. In this study, the plasma and spatter, which are generated during laser welding, are measured using UV and IR photodiodes. The factors that influence weld quality are classified into five categories; optimal heat input, slightly low heat input, low heat input, partial joining due to gap mismatch, and nozzle deviation. The data number deviated from reference signals and their standard deviations were also considered to evaluate the qualities. A system was also formulated to perform real time evaluations of the weld quality using a fuzzy multi-feature pattern recognition with the measured signals. 相似文献
12.
13.
14.
15.
Jong Chan Lee Jin Young Park So Young Yoon Yong Hun Bae Seung Jun Lee 《Tetrahedron letters》2004,45(1):191-193
A novel and direct method for the synthesis of α-halocarbonyl compounds using sequential treatment of carbonyl compounds with [hydroxy(tosyloxy)iodo]benzene followed by magnesium halides under solvent-free microwave irradiation conditions is described. 相似文献
16.
本文改进实验方法,在0.0001—1.23GPa流体静高压下测量了整片非晶锂离子导体B2O3-0.7Li2O-0.7LiCl-xAl2O3(x=0.05;0.15)及其粉末压片的离子电导率及激活体积。发现粉末压片电导率峰值是由非晶微粒间的接触电导及非晶微粒体电导两者叠加;对整片非晶电导率的压力效应用离子迁移通道的物理图象给出初步的微观解释。此外,还观测到氧化铝组分减少使电导率的压力转变点明显降低;测量出不同温度热处理以及300℃等温热处理4—20h后离子电导率-压力曲线的变化规律,仍可归因于非晶态相分离及两种非晶相的先后晶化。
关键词: 相似文献
17.
Myungjin Jeon Dongsoong Han Kyeongsu Park Gundon Choi 《Journal of Applied Mathematics and Computing》2005,18(1-2):235-246
We present an interpolating, univariate subdivision scheme which preserves the discrete curvature and tangent direction at each step of subdivision. Since the polygon have a geometric information of some original (in some sense) curve as a discrete curvature, we can expect that the limit curve has the same curvature at each vertex as the control polygon. We estimate the curvature bound of odd vertices and give an error estimate for restoring a curve from sampled vertices on curves. 相似文献
18.
We have rigorously calculated for the first time all the inter-electrode and pixel capacitances of Thin-Film Transistor Liquid Crystal Displays using the electrical energy distribution inside a liquid crystal cell. The energy distribution is obtained from the three-dimensional profiles of potential distribution and molecular director. The dynamic equation of continuum theory for liquid crystals is described in a tensorial form in order to maintain the equivalence of n and -n . The effects of lateral fields generated by multiple electrodes of finite sizes are taken into account in the simulation. As a numerical technique, we used a finite difference method which is suitable for the highly non-linear equations. As a result, we confirmed that the pixel capacitance for our pixel structure is about 40% larger than that of the conventional approach. It is also revealed that the gate-common and gate-data inter-electrode capacitances are not negligible. 相似文献
19.
S. H. Park J. H. Chang M. Yang H. S. Ahn S. N. Yi K. Goto M. W. Cho T. Yao J. S. Song 《Current Applied Physics》2004,4(6):607-610
Photoluminescence (PL) linewidth broadening of CdxZn1 − xSe/ZnSe triple quantum wells, grown on GaAs substrates by molecular beam epitaxy (MBE), has been investigated. Various quantum well (QW) samples have been prepared with different QW thickness and composition (Cd-composition). Measured and calculated PL linewidth are compared. Both composition and thickness fluctuations are considered for the calculation with the parameters such as the volume of exciton, nominal thickness and composition of QWs. Surface roughness measured by atomic force microscopy (AFM) is used to estimate the interface roughness. Results show that when Cd-composition increases additional linewidth broadening due to Zn/Cd interdiffusion is enhanced. 相似文献
20.
从现行典型园区网络安全设计方案入手,结合其在安全防范解决方案上存在的问题,提出了一种网络主动安全模型;在全局网络安全认识的基础上.阐述了模型组成部件的功能定义和网络主动安全实现流程;采用统一网络入口认证、网络知识发现及资源有效控制、沟通等手段,解决了现行网络安全设计中存在的恶意攻击行为源头定位困难,以及信息安全司法取证不准、网络资源安全被动防护、网络灾难快速反映能力差等问题.实验结果表明,该设计方案具有较好的可行性和实用性. 相似文献